Fans have been used for many years for a wide variety of purposes and are designed in an equally wide variety of configurations. Various attempts have been made to control the operation of fans and/or to provide some form of failure or fault detection. Such attempts have included differential pressure switches, downstream pressure switches, motor RPM sensors, current sensors, and the like. For the most part, most such approaches are fairly complicated, add undesirable weight to the fan package or considerably add to the package or envelope size. All of these factors are undesirable and cause problems in aerospace applications where simplicity, size and weight are critical parameters.
Furthermore, in aerospace applications, reliability is of paramount importance. Differential pressure switches are difficult to predict and calibrate. Sophisticated aerospace fan structures usually are self-contained and totally enclosed packages, and downstream pressure switches sometimes do not give an accurate indication or are not responsive to the air flow in the fan air stream conduit or involute itself. RPM sensors may sense fan rotation even though the fan fails because of low or no flow in the fan involute, itself. Ease of installation and maintenance also are critical in aerospace applications where such prior approaches are unacceptable.
There is a definite need for a fan structure with a flow responsive switch mechanism which is simple, small and lightweight, easy to install and maintain and very reliable in indicating fan performance. For instance, in aerospace applications, activation of the switch can be used to provide a signal indicating the sufficiency or insufficiency of air flow through the fan, or the switch can be used in a servo-type system to respond appropriately to the presence or absence of sufficient air flow through the fan.
This invention is directed to satisfying these needs and solving the problems of prior fan controls.